That's great she will trade you back! Some breeds it's harder to tell because the hens have large combs. Like my australorps. I swore at least one was a roo. One was tail-less for way too long and that means roo with that breed. Well, she lays, lol. They had large red combs and wattles while yound. I don't know what fbcm stands for? Can you find pics online to compare. Sometimes only time will tell, but as you get used to the breed you can normally spot the roos by comb/wattles color and growth. Some pics would help? Ya have any?